1. Field of the Invention
The present invention relates to bearing resin material. More particularly, the present invention relates to resin material in which the fiber is incorporated, and which is occasionally impregnated with lubricating oil.
2. Description of the Related Art
Phenol resin, polyamide resin (nylon), fluorocarbon resin, polyacetal resin, polycarbonate resin, and the like are conventionally used as the basic material for low-grade bearing materials. Lead, graphite, MoS.sub.2, fiber, and the like are incorporated into one or more of these resin materials to enhance the sliding characteristics thereof. So-called plastic bearing materials are also conventionally used, and the fibers conventionally incorporated into the plastic bearing materials are carbon fiber, glass fiber, and cotton.
It is known to incorporate the polyacetal with lubricating oil in the field of oleo-bearing materials. Japanese Unexamined Pat. Publication No. 46-5321 discloses a method for producing an oleo-bearing material having a uniform distribution of the lubricating oil.
The disclosed method essentially resides in heating the thermoplastic resin to a temperature higher than the softening point, stirring in lubricating oil, and then allowing it to cool.
It is also known in the field of plastic bearing materials to fill the plastic with the polytetrafluoroethylene (PTFE) to enhance the sliding characteristic.
The present inventors investigated the characteristics of the conventional bearing materials from the viewpoint of improving the sliding characteristics.
In general, the plastic bearing materials are more advantageous than metal bearing materials from the standpoints of lighter weight and elimination of the necessity for lubrication during use, but the plastic bearing materials are less advantageous than the metal bearing materials from the standpoints of a lower strength and lower PV-value, and hence are not practical for use under a great load. If the disadvantages of the plastic bearing material(s) (hereinafter referred to as the "bearing material(s)") can be overcome while maintaining their advantages, they could be used over a broader field than at present, and a great contribution could be made to enhancing the properties and reliability of the bearing devices.
Lead, MoS.sub.2, graphite and the like, which are incorporated in the resin as the basic component of the bearing materials, cause a reduction in the coefficient of friction but virtually do not contribute at all to strengthening the resin. In fact, lead and the like decrease the strength of the resin. In addition, the coefficient of friction is increased under a high load. The bearing materials having lead and the like incorporated therein are therefore disadvantageously liable to seize under a high load.
Glass fiber, carbon fiber, cotton and the like, which are conventionally incorporated into the bearing materials, give a fiber-reinforcement to the materials but cause a conspicuous wear of the other materials in the bearing device. In addition, the amount of wear in the bearing materials per se is high. Among the above mentioned fibers, cotton causes a relatively small amount of wear in the bearing materials and the other materials. Such an amount of wear is, however, still unsatisfactory. The conventional fiber-incorporated bearing materials exhibit a high coefficient of friction and a low PV value under thrust loading test conditions.
The conventional oleo-bearing materials are superior to the bearing materials free of fibers from the stand points of their coefficient of frictions and wear resistance. Their loading capacity is, however, unsatisfactory. The coefficient of friction tends to increase under a high load and, therefore, the conventional oleo-bearing materials are liable to seize under a high load. Regarding the loading capacity and the sliding characteristics under a high load of the oleo-bearing materials, since they are superior to those of the fiber bearing materials, the oleo-bearing materials can be used under relatively severe conditions. If it is intended to use the oleo-bearing materials under more severe conditions, similar to those under which metal bearing materials can be used, it would become obvious that, in comparison, the sliding characteristics of the conventional oleo-bearing materials are unsatisfactory, and such unsatisfactory sliding characteristic cannot be overcome by impregnating the lipophilic fiber with oil.